DESCRIPTION: Individuals with mental retardation show impairments on many perceptual and cognitive tasks that require the accurate encoding of the temporal characteristics of, and relationships between, sensory stimuli. Recent work suggests that these impairments may be greater on tasks that more selectively target the "transient" visual pathways, however no study has explored this directly with methods designed to characterize the hypothetical impairment. Previous observations consistent with a temporal processing impairment may reflect inefficient function at one or more stages in the flow of visual information processing. No studies to date have attempted to identify the stage or stages at which a temporal processing impairment may reside. In this proposal, a set of experiments [are] proposed to characterize the visual temporal processing abilities of individuals with mental retardation using three different levels of analysis: 1) Visual-sensory temporal processing: The Critical Flicker Fusion (CFF) task will be used to characterize visual temporal sensitivity. The CFF predominantly reflects the functional properties of the visual system pathways sensitive to transient information and performance on this task is mediated little by cognitive processes; 2) Time perception: A duration discrimination task, where individuals are required to make discriminations about the perceived durations of visual stimuli, would be used to characterize this aspect of visual temporal processing. Performance on this task is thought to reflect an internal time-keeping mechanism or "internal clock;" and 3) Time estimation. Perceptual judgments of long stimulus durations are believed to reflect predominately cognitive processes, rather than sensory or perceptual processes. The proposed studies are designed to be an initial assessment of these abilities which would serve to guide future investigations by revealing the stage(s) in visual information processing where individuals with mental retardation may have a temporal processing impairment.